Process for the manufacture of cement



Patented Dec. 1, 1931 UNITED STATES PATENT OFFICE OSCAR NICKEL, OFMULHEIM-RUHR, AND REINHOED MARKWI'IZ, OF DUISBURG, GERMANY PROCESS FORTHE MANUFACTURE OF CEMENT No Drawing. Application filed June 3, 1924,Serial No. 717,578, and in Austria May 18, 1922.

The present invention relates to a process for the manufacture of cementfrom slag and other dry substances containing silicates, such as naturalminerals or waste products.

Numerous processes have been suggested and are known, for producingcement by means of the reaction between line and substances containingsilicic acid or silicates. Furnace slag especially (such as blastfurnace slag) has frequently been employed for this purpose. However,the procedure has always been started fromthe point of view that, in thefinished cement, a certain reciprocal action must take place between theacid and basic components, that is between the silicates and the lime inthe presence of moisture, if the finished cement was required to possessthe desired firm binding or setting properties.

Thus it has been suggested to grind granulated furnace slag togetherwith slaked lime, the slag containing water is received from thegranulating process has most commonly been used for this, on the onehand, to avoid the need of a drying process, and on the other hand,because of the idea that the quicklime,

when added to it and ground with it, would exercise a certain openingeffect on the silicate, owing to the heat generated by the reaction ofthe lime with the water contained in the slag, thereby giving theproperties of cement to the finished mixture. Also the taking up ofwater by the quick-lime has been made use of for drying the granulatedslag. In cases where the water content of the watergranulated slag hasbeen reduced considerably, i'or example, owing to its having been storedfor some time, it has even been considered necessary to add considerablequantities of water to the mixture of the granulated slag and lime,either during the process of grinding or afterwards. This water wasadded with the idea that the normal water content of the granulated slagwas necessary for reacting with any quick lime present.

According to the present invention, a cement of quite excellentproperties and of surprising keeping qualities is obtained by theemployment of technically dry furnace slag, or similar siliciousmaterial (other metallurgical slag, boiler slag, trass, tufa, and so on)which is ground together with burned unslaked lime, to the fineness ofcement. We call attention to the fact that the granulated slag is in adry state. By this, we do not mean that the slag is absolutelyanhydrous, but it should not contain substantially more than, say, 3%moisture.

We regard slags as technically dry, when the water content does notexceed 3%. The water content cannot be cheaply reduced much below 1%,even when the slag matcrial is heated for some time over 100 C., so thatit is no longer possible to detect any escape of moisture. It appears asif a small amount of water remains in combination as water of hydration.Naturally, -for the process in question, the slag can also be dried, asif by analysis, i. e., the water content be reduced to 0%. such ananhydrous condition could probably be attained only at a low red heat.This is excluded for economic reasons and the slag would also be indanger of undergoing devitrification. But the slag must be technicallydry, the water content not appreciably e: :cceding 3%. The sameconditions exist for pumice stone and tuia. The drying of these latteris somewhat more difficult, but here, also, the highest permissiblelimit is between 3% and F/O. \Ve make no claim to treating granulatedslag in a wet state with lime, nor to the treatment of slaked lime withwet or dry slag.

In addition to the above materials, technically dry silicate andunslaked lime, we

also cm 310 W )sum sa about 1 to 5% of 1e entire mixture, this materialbeing prefrably used in its natural condition, that is, without previouscalcination. It is preferably ground with the other two materials.

The proportion of lime to silica used in making the cement, socalculated that the entire lime content of the finished cement(including that contained as a constituent of the slag) ranges fromabout 50 to 56%. With low percentage of alumina, it is about 50%. With ahigh percentage of alumina, it is about The present application is apart continu- But ation of our copending application filed July 28,1922, Serial No. 57 8,223.

It has been found that the keeping quali ties of the cement aredependent to an important extent'on the absence of hydrates of lime,hence: the need of previously drying thematerialsf The ingredients canalso be 1 ground first separately and mixed afterwards; however,grinding together is more 10 practical.

In place of the quick-lime of more orlesshigh percentage, hydraulic limecan be used, 7 provided it does not contain any silicates.

As to the matter ofproportions, thepr-eferred proportions Will varyconsiderably,

depending on thecompositionof the silicate materials to be used.Thus'.the following examples are given, for illustration, and-not asrestricting the invention theretoiz, p I Example 1 Zito 5- pantsofgypsum 3 to 16 parts of unslaked lime '95 to 79 partsof driedWater-granulated blast 5 -1- furnace slag.

p Emamqvle 2-to 5 parts of gypsum .6 to-QO parts o'l' unsla-ked burnedlime 90 to? 5 parts of dried Water-granulated slag from copper smelting;

E agample 3 I .2 toiiparts of gypsum B GtoQO parts of unslaked burnedlime 92' to 7.5 parts .ofdried pumice or trass.

' We claim: o Cement comprising-a mixture ofabout 3 to %of burnedunslaked lime, about to'95%. of substantially dried WZltOF-gl'illllk.lated furnace slag, and about 1 to 5% of gypsum, all ground toapproximately the fineness of ordinary cement.

In testimony whereof We aflix our signa- JJturesL f OSCAR NICKEL. REI-NHOLD MARKWITZ.

